Sucrose Accumulation and Maturity

Appears in

Oxford Companion to Sugar and Sweets

Oxford Companion to Sugar and Sweets

By Darra Goldstein

Published 2015

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In the stalk, starch formation and storage occupy a greatly reduced role, presumably due to breeding and selection for varieties with enhanced stored sucrose levels. Sucrose, therefore, dominates as an accumulating end product and is transported from the leaves to the stalk via the phloem. Sucrose accumulation can be increased by factors such as environmental stress (incident sunlight, water, nutrients, and temperature), application of chemical ripeners, and planting density or arrangement. The phenomenon of ripening occurs when growth or stalk elongation ceases or slows, along with the accumulation of sucrose in tissues developed during the growth phase. Therefore, conditions that promote growth are not conducive for sucrose accumulation. Plant maturity also has a role in the relative rate of sucrose accumulation since, in the early stage of growth, plant tissues contain high levels of nitrogen, moisture, invert sugars, and enzymes, while operating with enhanced nitrogen metabolism and respiration rates. The process of aging eventually produces conditions where there is a gradual exhaustion of nitrogen and water with lowered reducing sugars, namely glucose and fructose, and reduced activities of the enzymes, resulting in the accumulation of sucrose. Thus, cane maturity is a function of variety and nitrogen and moisture status, but it is unpredictably complicated by climatic parameters such as light, temperature, rainfall, and humidity. Adding to this complexity is the fact that different varieties of sugarcane possess different sensitivities to the stresses that alter the rates of photosynthesis, structural growth, and sucrose accumulation. In some sugarcane-growing regions of the world, normal ripening does not occur for whatever reason, and interest is widespread in developing chemical methods to induce or increase ripening, or to enable its synchronization with harvest. Most chemical ripeners are growth regulators or herbicides that are applied in sublethal doses, which induce ripening by chemically restricting growth, allowing the plant to accumulate sucrose.